The invention relates to a drive cartridge comprising an actuating mechanism, in which a spindle can be guided in a hollow cylindrical drive element between two end positions and an axial distance from another, said positions being defined by the axial length of the drive element; and to a dome-shaped casing that surrounds the drive element in a non-rotatable and non-displaceable manner.
In particular in the area of industrial water and/or waste water, pipeline systems made of thermoplastic polymers, such as polyethylene, are preferred, since they are durable, resistant to corrosion and easy to handle. Also certain components, such as shut-off fittings, are manufactured from thermoplastic polymers to a large extent for optimal connection to the pipeline system.
DE 10 2006 030 027 A1, for example, shows a shut-off fitting of which the housing can be manufactured from a thermoplastic polymer, such as polyethylene, wherein the actuating mechanism and a sleeve surrounding said actuating mechanism consist of metal. An upper and a lower stopper means made of metal signal the open end closed positions of obturators which are actuated by means of said actuating mechanism. This metal sleeve, also referred to as a dome, is molded with a thermoplastic polymer so that bonding to the housing is possible and thereby forms, as a sub-assembly of the shut-off fitting, a drive cartridge which is connected to said housing by means of electrofusion technique. In order to prevent that said metal sleeve separates from the surrounding polyethylene due to occurring stresses, the sleeve is provided on its outer surface with toothings which form indentations into which the polymer penetrates. Although a failure proof bonding between metal and polymer is ensured thereby, manufacturing of the metal sleeve, however, is complex and intricate.
In the shut-off valve described in EP 0 711 947 A, the metal valve housing is also molded with polymer, wherein circumferential grooves are provided to enhance anchoring. To prevent rotation of the valve housing within the polymer, it is formed a hexagon along at least a part of its length.